Couple of points:

1) I understand the use case, but asking people to trust you with their twitter credentials is bad news bears. Isn't some combination of OpenID/OAuth supposed to fix this (once twitter gets around to it, or whatever)?

2) I think the intersection of digg with twitter is interesting (don't know if it is novel), and using a tweet tag is a clean way to do it.

3) Your design is pretty clean, don't know if I like the color scheme or name though.

4) Is "thoughtful tweet" an oxymoron? Is there a good use case for high SnR microblogging?